Serine proteases play a critical role in many physiological processes. For example, serine proteases are involved in blood coagulation, fibrinolysis, complement activation, and inflammation. The catalytic activity of these serine proteases is often regulated by members of a super-family of serine protease inhibitors called serpins. Serpins act to regulate the activity of serine proteases by binding stoichiometrically to the active sites of serine proteases and thus inactivating the enzymes. See Carrell, et al. (1987) Cold Spring Harbor Symposia, vol. LII, pp. 527-535 for a description of the general structural characteristics of serpins.
Many serpins are extracellular proteins which regulate extracellular processes such as blood coagulation, fibrinolysis and complement activation. In addition, there is a family of serpins structurally related to ovalbumin which lack secretory peptide sequences and which may function, in part, intracellularly. Several of this latter group of serpins are believed to play an important role in regulating serine protease activity in inflammation. Elastase inhibitor is an example of such a serpin which functions to regulate the activity of neutrophil elastase. Neutrophil elastase is stored in the azurophil granules of neutrophils, monocytes and macrophages, and degrades both phagocytized and extracellular substrates. Regulation of neutrophil elastase is important both in host defense mechanisms and also in the pathology of diseases such as arthritic joint diseases.
Interleukin-1.beta. converting enzyme (ICE) is an another example of a cysteine protease that plays an important role in inflammation. ICE is responsible for the activation of interleukin-1.beta., which is a critical cytokine in the inflammatory process. Serpins which inhibit ICE may therefore play an important role in inflammation. One such serpin is a viral protein encoded by the cowpox virus crmA gene. It is believed that expression of crmA protein inhibits ICE and thereby blocks migration of inflammatory cells in cowpox lesions. (See Ray, C. A., et. al. (1992) Cell 69:597-604.) Isolated cellular serpins that inhibit ICE in a similar manner to the crmA protein can be useful in the modulation of the inflammatory response. Agents that modulate the inflammatory response can be used in the treatment of a variety of inflammatory diseases, such as rheumatoid arthritis.
ICE is but one member of a family of serine proteases that play important roles in normal physiology and in pathophysiology. For example, another member of the ICE family, Ich-1, is involved in regulation of apoptosis. Furthermore, evidence is accumulating that regulation of apoptosis plays a role in a variety of different diseases, including cancer. Therefore, isolated serpin molecules which inhibit Ich-1 could be used to regulate apoptosis and treat a number of diseases.
Isolated serpin molecules are also useful in the purification of a variety of proteins for use in medicine and industry. Protein degradation during purification by endogenous serine proteases is a common problem. Isolation of serpins inhibiting different serine proteases is useful to improve the purification of many different proteins. These and other needs are addressed by the present invention.